PRECISE SCANNING CALORIMETER FOR STUDYING THERMAL-PROPERTIES OF BIOLOGICAL MACROMOLECULES IN DILUTE-SOLUTION

A precise scanning calorimeter for studying the heat capacity of liqui ds in a broad temperature range has been developed. By its design and capabilities this calorimeter is the first of a new generation for thi s type of instrument. This new scanning calorimeter operates different ially, is equipped with a pair of gold capillary cells and semiconduct or sensors, and is able to scan up and down in temperature at user-sel ected rates. This instrument is completely operated by an integrated c omputer which also provides a full thermodynamic analysis of the resul ts. Its construction does not involve the use of organic compounds, th us eliminating a source of baseline noise that has affected previous c alorimeters. The operational temperature range of the instrument can b e varied between 0 and 120 degrees C. The gold capillary cells (operat ional volume 0.8 ml) minimize temperature gradients in the heated/cool ed liquid sample and permit easy washing and reloading without air bub bles. These features are crucial for the accuracy of difference heat c apacity measurements and determination of the absolute value of the pa rtial heat capacity of solute molecules. The measurements can be perfo rmed under an excess constant pressure (up to 3 atm) to prevent format ion of gas bubbles and boiling of aqueous solutions above 100 degrees C. The noise level of the recorded heating/cooling power difference is below 50 x 10(-9) W (i.e., below 10 ncal/s) with a response half-time of 5 s. The reproducibility of the baseline without refilling the cap illary cells is on the order of 0.5 x 10(-6) W. Reproducibility of the baseline upon refilling the cell is of the same order of magnitude. T his provides an accuracy in difference heat capacity determination on the order of 10 mu cal/degrees Kml at a heating rate of 1 degrees K/mi n. (C) 1995 Academic Press, Inc.